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Elements Described in Terms of their Atoms?   
Lesson 3.1

Key Concepts
  • How are elements described in terms of their atoms?

Key Terms
  • protons
  • neutrons
  • electrons
  • atomic number
  • isotopes
  • mass number
  • model

How are elements described in terms of their atoms?

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Number of Protons
  • Each element is made up of atoms that differ from the atoms of other elements.
  • An element can be identified by the number of protons in the nucleus of its atoms.

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Atomic Number
  • Every atom of an element has the same number of protons. This unique number is called the atomic number.
  • It is equal to the number of protons in the nucleus of an atom.

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Isotopes
  • Although all atoms of an element have the same number of protons, they may have different numbers of neutrons.
  • Isotopes are atoms with the same number of protons and a different number of neutrons.

Picture
 
        Mass Number
  • An isotope is identified by its mass number, which is the sum of the protons and neutrons in the nucleus of that atom.
  • Although isotopes have different mass numbers, they react the same way chemically.
Structure
Element Description
Models

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